Such liners are pulled on over an amputation stump of the patient before said amputation stump is inserted into a rigid prosthesis socket. The prior art discloses various possible ways of securing the prosthesis socket, and therefore the prosthesis itself, on the amputation stump of the patient or on the liner which is worn over the amputation stump. A widely used method is one in which a volume is defined between the liner and the prosthesis socket and is closed off to be as airtight as possible, and an underpressure is built up within this volume and ensures that the prosthesis socket is sucked firmly onto the liner. Such a liner is known from WO 2009/062489 A1, for example. The inner face in this case bears on the amputation stump, while the outer face is in contact with a prosthesis socket, for example. The adherence to the amputation stump and to the prosthesis socket is improved by the liner being designed with an inner liner and with an outer liner. In particular, the proximal portion of the outer liner can be turned back over the proximal edge of the prosthesis socket.
Since leakages and slight seepage can always cause more air to flow into the volume that has thus been evacuated, it is important to ensure that the underpressure in this volume between liner and prosthesis socket is constantly maintained. In addition, for different modes of movement and forms of actuation of the amputation stump, it is expedient to generate and maintain different degrees of underpressure in the volume. For example, when walking using a below-knee prosthesis, it is necessary to generate a much stronger underpressure in the volume than is needed when the person wearing the prosthesis is seated, for example.
The prior art discloses a number of ways of maintaining the underpressure. Initially, the volume was evacuated, for example, by an electrically operated pump. However, this has a number of disadvantages. On the one hand, this means that the person wearing the prosthesis has to carry around the additional weight and volume of the pump and, on the other hand, the pump has to be provided with a constant supply of power, for example by batteries. In addition, the pump causes an annoying noise to develop, which detracts from the overall wearing comfort of the prosthesis.
For this reason, the separate, electrically operated pump was replaced in many designs by a mechanical pump in which the movement of the liner or of the amputation stump located in the liner is used to evacuate the volume between the liner and the prosthesis socket. Such designs are known, for example, from U.S. Pat. No. 8,197,555 B2 and US 2012/0191217. Both documents describe prostheses in which, in the distal area of the liner, a volume is present between the liner and the prosthesis socket, which volume is compressed in the loaded state, for example when standing. Air located in the volume is in this way forced through a one-way valve located in the prosthesis socket. In this way, the pressure in the interior of the volume is reduced and, consequently, the underpressure is maintained.
DE 10 2006 054 891 A1 discloses a cup-shaped prosthesis socket in which, in the posterior area, a flexible chamber formed by films is arranged in the interior of the prosthesis socket. This chamber too is compressed during walking movements, such that air contained in the chamber is forced out of the prosthesis socket via a dedicated outlet line, which is routed through the prosthesis socket, and via a one-way valve arranged on said outlet line. However, in contrast to the aforementioned embodiments, the pump chamber here is not arranged in the distal area of the amputation stump.
The function of such a pump, which uses the movement of the amputation stump to evacuate a volume, is described in EP 1 771 659 B1, for example. The interior of the pump chamber accommodates, for example, an elastically deformable material that applies the restoring force and thus ensures that the pump chamber deploys again in the unloaded state and receives air from the volume to be evacuated.
U.S. Pat. No. 8,357,206 B2 and US 2012/0191218 A1 each disclose a liner which is provided with a distributing or conducting layer on the outer face of the liner. This layer consists of a porous and gas-conducting material and in this way forms a pump chamber distributed across almost the entire amputation stump. Alternatively, a separate external pump can also be attached which sucks air and optionally moisture out of the distributing or conducting layer. In US 2012/0191218 A1, the liner in the distal area of the amputation stump is additionally porous or provided with a multiplicity of holes or passages in order thereby to remove liquid from the amputation stump.
However, in these embodiments too, an outlet valve and an outlet channel are needed, which are routed through the prosthesis socket in order to convey the air out of the volume that is to be evacuated between liner and prosthesis socket.
The one-way valves and outlet lines or outlet channels, which are needed to carry away the air removed from the volume by the pump, are generally arranged in the distal area of the prosthesis socket, the overall height of which is thereby increased and its construction thereby complicated. Since the prosthesis socket is adapted individually to the person wearing the prosthesis, it is desirable that the orthopedic technician performing this adaptation is able to make available a prosthesis socket that otherwise has the simplest possible configuration. Particularly in the case of amputations a short distance above the knee for example, it is necessary that the prosthetic knee adjoins the distal end of the prosthesis socket directly, and therefore the space available for an elaborate valve arrangement is inadequate in these cases.